Question 211578
The height of a projectile fired upward with an initial velocity of 400 ft per sec is given by the formula h=-16t^2+400t, where h is the height in ft and t is the time in sec. Find the time required for the projectile to return to earth.
:
 h = -16t^2 + 400t
When the projectile returns to earth, h = 0, therefore:
 -16t^2 + 400t = 0
factor out -16x
-16t(t - 25) = 0
our solution
t = 25 sec to return to earth
:
:
Check solution in original equation
 -16(25^2) + 400(25) =
-16(625) + 10000 =
-10000 + 10000 = 0